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Session 2 Excercises: Hands on with Python and/or R


Getting started with R

  • Download R and RStudio
    • Follow directions here if you need help (don't worry about the "SDSFoundations" stuff)
  • Go over R_intro.R file

Getting started with Python

  • For absolute beginners, download and install Thonny
  • If you are interested in Jupyter Notebooks or plan on doing a lot of data analysis in Python, consider downloading Anaconda. I recommend installing Python versions >= 3.5.
    • It handles the installation of almost all scientific computing Python packages (Numpy, Pandas, Scipy, Scikit-Learn, NLTK).
    • It makes it very easy to get up and running with Jupyter.
    • It also includes a fully-featured Python IDE called Spyder (may be more comfortable for users coming from RStudio)

Personal Exercises

For these exercises, choose the lanuage you would like more familiarity with.

Beginning Python and R

For beginners (of either language), I highly recommend working through a set of simple tasks that stretch your understanding of functions, inputs, lists, and iteration (i.e., for loops). Proceed through the following list of tasks:

  • Write a function that prints "Hello, World!"
  • Write a function that takes the user's name as input and greets them with by name.
  • Write a function that takes an input n and prints the sum of the numbers 1 to n.
  • Write a function that returns the largest element in a list.
  • Write a function that returns the elements on odd positions in a list.
  • Write a function that computes the list of the first 100 Fibonacci numbers .

I wrote answers to most of these tasks here: (answers).

If you have more downtime and want to dedicate some time to learning your language of choice, here is a longer list of good programming challenges.

Intermeidate Python and R: General Scripting

  • For R: Construct a new data.frame from the ascii.txt file, in which every row corresponds to a line in the file, and the columns represent the counts of the characters contained in each line.
  • For Python: Construct a list of dictionaries containing the letter counts for each row (i.e., each row is entry in the list, which is a dictionary containing the counts of each letter on that line)
  • For example, in the example below, the first row has 3 X's and 2 Y's, whereas the second row has 1 X, 3 Y's, and 1 Z
XYYXX    
XYZYY 

The resulting dataframe for this string is:

   X Y Z
1  3 2 0
2  1 3 1

And the results Python list would be:

[
	{"X": 3, "Y":2},
	{"X": 1, "Y":3, "Z": 1}
]

Tips!

Use Google! Use StackOverflow!

For R users

  • To read the rile into R as a string, use the read_file function from the readr package:
install.packages("readr")
library(readr)

setwd("/path/to/week1/") # change working directory to the week1 folder
# NOTE for Windows users! Filepaths should use backslashes instead of forward:
setwd("C:\\path\\to\\week1")

ascii_txt = read_file("ascii.txt")
  • The stringr package has a nice function called str_count(string, pattern), which counts occurrences in a string. HOWEVER! By default it uses regex to match strings. Because there are special regex characters in the document we are scanning, instead use the function stri_count_fixed from the stringi package, which has the exact same format but does exact string matches rather than regex matches.

For Python users

  • To read the file as a string into your program, use the following notation:
import os

os.chdir("/home/path/to/week1") # change working directory to the week1 folder
# NOTE for Windows users! Filepaths should use backslashes instead of forward:
os.chdir("C:\\path\\to\\week1")

with open("ascii.txt") as file:
	ascii_txt = file.read()
  • This consider using split and the set function, which returns only unique items in an iterable object (i.e,. a list or tuple).

Bonus points!

  • Wrap your calculations in a function that can do the same for any text file. Then perform the same character counting calculation for the intro.sh file.

Intermediate R: Munging Data

  • Copy and paste the code below to construct two time-series dataframes, one consisting of data from the US and one from the UK
if (!require("zoo")) install.packages("zoo")
US = USAccDeaths
US = data.frame(date = as.Date(as.yearmon(time(US))), US_Data = coredata(US))

UK = UKDriverDeaths
UK = data.frame(date = as.Date(as.yearmon(time(UK))), UK_Data = coredata(UK))

head(US)
head(UK)
  • Your task is to construct a single dataframe, that has:
    • the date in one column
    • the US_Data in one column
    • the UK_Data in another column.
  • You can drop any dates in the UK dataset that are not contained in the US dataset.
  • Additionally, for fun, make time-series plots of the data. I.e., plot the US_Data on the Y axis with date on the X axis.
    • Make a line plot using plot(x=X_DATA, y=Y_DATA, type="line")
  • DOUBLE BONUS POINTS! Plot both US and UK data on the same plot.